clk: rockchip: Fix fractional PLL calculation for RK3588

RK3588/RK3576 have several fractional PLLs using a delta-sigma adjustment
factor (k) for the fractional component of the PLL output frequency.

According to the TRM, the k is a two's complement 16-bit value, not an
unsiged integer (see for example the TRM description of CRU_GPLL_CON2,
and also a related U-boot fix at [1]).

Adjust the code to properly handle negative k values.

While at it, also fix the denominator to use the correct value of 65536,
not 65535 for the full range of PLL ratios.

Cc: stable@vger.kernel.org
Fixes: 8f65944 ("clk: rockchip: add pll type for RK3588")
Link: https://lore.kernel.org/all/20231012101828.27195-1-zhangqing@rock-chips.com/ [1]
Signed-off-by: Alexey Charkov <alchark@flipper.net>

Author: alchark

drivers/clk/rockchip/clk-pll.c

@@ -13,6 +13,7 @@
 #include <linux/delay.h>
 #include <linux/clk-provider.h>
 #include <linux/iopoll.h>
+#include <linux/math64.h>
 #include <linux/regmap.h>
 #include <linux/clk.h>
 #include "clk.h"
@@ -897,7 +898,7 @@ static void rockchip_rk3588_pll_get_params(struct rockchip_clk_pll *pll,
 	rate->s = ((pllcon >> RK3588_PLLCON1_S_SHIFT) & RK3588_PLLCON1_S_MASK);
 
 	pllcon = readl_relaxed(pll->reg_base + RK3588_PLLCON(2));
-	rate->k = ((pllcon >> RK3588_PLLCON2_K_SHIFT) & RK3588_PLLCON2_K_MASK);
+	rate->k = (s16)((pllcon >> RK3588_PLLCON2_K_SHIFT) & RK3588_PLLCON2_K_MASK);
 }
 
 static unsigned long rockchip_rk3588_pll_recalc_rate(struct clk_hw *hw, unsigned long prate)
@@ -913,11 +914,10 @@ static unsigned long rockchip_rk3588_pll_recalc_rate(struct clk_hw *hw, unsigned
 
 	if (cur.k) {
 		/* fractional mode */
-		u64 frac_rate64 = prate * cur.k;
+		s64 frac_rate64 = prate * cur.k;
 
-		postdiv = cur.p * 65535;
-		do_div(frac_rate64, postdiv);
-		rate64 += frac_rate64;
+		postdiv = cur.p * 65536ULL;
+		rate64 += div_s64(frac_rate64, postdiv);
 	}
 	rate64 = rate64 >> cur.s;
 

drivers/clk/rockchip/clk.h

@@ -638,7 +638,7 @@ struct rockchip_pll_rate_table {
 			unsigned int m;
 			unsigned int p;
 			unsigned int s;
-			unsigned int k;
+			int k;
 		};
 	};
 };